This research will utilize ultrastructural studies of tissues of the middle ear in both normal and diseased states. Bats will be used as a normal, healthy experimental animal since they have acoustic mechanisms delicately coordinated with sound production in the phenomenon of echolocation. A second facet of the study will concentrate on the cytologic changes that characterize otosclerosis, a common disease of the middle ear in man. It is planned to: (1) complete the final stages of correlation of the cytology of rapidly conctracting tympanic muscle with those of synchronously active muscles of the larynx in echolocating bats; (2) study the cytologic features of normal ossicles and joints in the middle ear of bats and in man; (3) evaluate the pathologic changes that are present in otosclerotic bone in man.